P0870-OD HYDRAULIC PRESSURE TEST





For a complete wiring diagram Refer to Section 8W

Theory of Operation


The Transmission Control System tests the pressure switches when they are off. The test verifies that the switches are operational (They will close with pressure applied). The Transmission Control System verifies that the switch closes when the corresponding element is applied. If a switch fails to close, it is re-tested. If it fails the second test, the DTC will set, the MIL will illuminate and the transmission system will default to the orderly Shutdown routine.


  • When Monitored:

    In any forward gear with engine speed above 1000 rpm shortly after a shift and every minute thereafter.

  • Set Condition:

    After a shift into a forward gear, with engine speed above 1000 rpm, the PCM momentarily turns on element pressure to the Clutch circuits that don't have pressure to identify the correct Pressure Switch closes. If the Pressure Switch does not close 2 times, the DTC sets.


Possible Causes
  
LINE PRESSURE SENSOR
  
TRANSMISSION FLUID CONTAMINATION
  
RELATED DTC'S PRESENT
  
TRANSMISSION SOLENOID/TRS ASSEMBLY
  
EXCESSIVE DEBRIS IN OIL PAN
  
POOR LINE PRESSURE SENSOR CONNECTION
  
RELATED TCM POWER INPUT DTCS PRESENT
  
(F856) 5-VOLT SUPPLY CIRCUIT OPEN
  
TRANSMISSION CONTROL RELAY OUTPUT CIRCUIT OPEN
  
(F856) 5-VOLT SUPPLY CIRCUIT SHORT TO GROUND
  
(T9) OD PRESSURE SWITCH SENSE CIRCUIT SHORT TO ANOTHER CIRCUIT
  
TRANSMISSION SOLENOID/TRS ASSEMBLY
  
INTERNAL TRANSMISSION
  
POWERTRAIN CONTROL MODULE
  

Always perform the 45RFE/545RFE Pre-Diagnostic Troubleshooting Procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)



Diagnostic Test

1.CHECK FOR RELATED DTCS



Is there any Loss of Prime, TCM Power Input, and/or Line Pressure Sensor DTCs present?

Yes
  • Refer to the Transmission category and perform the appropriate symptom. If the DTC, P0944-LOSS OF PRIME is present, perform its respective test first.


No
  • Go To 2

2.CHECK IF DTC P0760 IS PRESENT



Is the DTC P0760 also present?

Yes
  • Refer to the symptom list and perform diagnostics for P0760-OD SOLENOID CIRCUIT.


No
  • Go To 3

3.CHECK FOR OTHER DTCS



Are any of the DTCs, P0733, P0734 ,P0735 and/or P0871 present also?

Yes


No
  • Go To 4

4.CHECK IF DTC P0870 IS CURRENT



Is the STARTS SINCE SET COUNTER 2 or less?

Yes
  • Go To 5


No

5.CHECK LINE PRESSURE







Did the line pressure remain at a steady value between 585 and 655 kPa (85 and 95 psi) in each position?

Yes
  • Go To 6


No

6.CHECK THE LINE PRESSURE SENSOR CONNECTION




Did the Line Pressure reading on the scan tool change to about 207 kPa (30 psi) when the connector was pushed inward?

Yes


No
  • Go To 7

7.CHECK THE LINE PRESSURE SENSOR OPERATION



CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.


WARNING: The Starter Relay must be removed from the PDC. Failure to do so can result in personal injury or death.


NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.






NOTE: All three scan tool Line Pressure readings should be steady and ±14 kPa (2.0 psi) of the reading specified on the Transmission Simulator.



Did the scan tool Line Pressure readings match the specified readings on the Transmission Simulator and remain steady in all three positions?

Yes


No
  • Go To 8

8.CHECK THE (F856) 5-VOLT SUPPLY CIRCUIT FOR AN OPEN






CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller tool #8815 to perform diagnosis.




Is the resistance above 5.0 ohms?

Yes


No
  • Go To 9

9.CHECK THE (F856) 5-VOLT SUPPLY CIRCUIT FOR A SHORT TO GROUND





Is the resistance below 5.0 ohms?

Yes


No
  • Using the schematics as a guide, check the Powertrain Control Module (PCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the PCM per the Service Information. With the scan tool, perform QUICK LEARN.
  • Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)

10.COMPARE SCAN TOOL TO PRESSURE GAUGE



CAUTION: Apply parking brake.




CAUTION: Do not overheat transmission.






Does the scan tool Line Pressure readings match the Pressure Gauge readings ± 10 psi?

Yes


No

11.CHECK PCM AND WIRING




CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.


WARNING: The Starter Relay must be removed from the PDC. Failure to do so can result in personal injury or death.


NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.







Did the OD Pressure Switch state change to closed and remain closed while wiggling the wires?

Yes


No

12.CHECK FOR EXCESSIVE DEBRIS





Does the Transmission Oil Pan contain excessive debris or contamination?

Yes


No

13.CHECK THE OD HYDRAULIC CLUTCH CIRCUIT


NOTE: The OD hydraulic clutch circuit contains a small bleed orifice which connects to the Reverse hydraulic clutch circuit. A small amount of air leakage is normal.



Was there excessive air leakage noticed during the air check?

Yes


No
  • Disassemble and inspect the Valve Body and repair as necessary. Inspect the OD Accumulator piston and seals. Check for an extra check ball downstream from the #6 check ball pocket and repair as necessary. If no problems are found in the Valve Body, replace the Transmission Solenoid/TRS Assembly per the Service Information.
  • Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)

14.CHECK THE (T9) OD PRESSURE SWITCH SENSE CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT





NOTE: Make sure the Transmission Solenoid/TRS Assembly harness connector is disconnected.




Is the resistance below 5.0 ohms between the (T9) OD Pressure Switch Sense circuit and any other circuit(s) in the Transmission Solenoid/TRS Assembly harness connector?

Yes


No
  • Using the schematics as a guide, check the Powertrain Control Module (PCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the PCM per the Service Information. With the scan tool, perform QUICK LEARN.
  • Perform 45RFE/545RFE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 45RFE/545RFE - STANDARD PROCEDURE)

15.CHECK WIRING AND CONNECTORS







Where there any problems found?

Yes


No
  • Test Complete.